n :  a theory in color vision: the eye has three separate elements each of which is stimulated by a different primary color
 
Young, Thomas (1773-1829), British physician, physicist, and Egyptologist. Young is remembered for his efforts to win broad acceptance for the undulatory theory of light. His research led him to the discovery of accommodation, the means by which the lens of the eye changes shape to focus on objects at differing distances, and to the discovery in 1801 of the cause of astigmatism. He also studied the problem of color perception and proposed that the eye does not have or need a separate mechanism for every individual color but only for three: blue, green, and red. Young's modulus was first defined by him in a lecture on passive strength and friction that appeared in print in 1807. Young is equally famous for being one of the first to translate Egyptian hieroglyphics. He began studying the Rosetta Stone in 1814, and after obtaining additional hieroglyphic writings from other sources, he produced a nearly accurate translation within a few years. His work was a major contribution to the deciphering of the ancient Egyptian language.
 
Helmholtz, Hermann Ludwig Ferdinand von (1821-1894), German physicist and physiologist. Helmholtz made fundamental contributions to physiology, optics, electrodynamics, and meteorology. He is best known for his statement of the conservation of energy, which he presented in 1847. He invented the ophthalmoscope in 1851, and he determined the mechanisms of focusing in the eye and of the motion of the eyeballs to give single vision. In 1852 he revived the theory of color vision that Young had first postulated in 1801-only to refute it. In 1858 he reversed his position, amending Young's original theory and becoming its foremost advocate. He also examined the structure and function of the organs and bones of the ear and developed the theory that harmonics are determinants of musical tone.
 
 
 
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